In automobile assembly lines, for example, an identification number is stamped on chassis frames and component parts (hereinafter referred to a frames) in order to identify and distinguish various types and models of vehicles produced on the lines. This serial number, which is commonly referred to as "frame number", is also used for post-production management (registration and policing etc.) of the serialized vehicles.
The frame numbers are stamped, according to prearranged production schedules, on successive frames being produced in an assembly line. It is crucial to avoid stamping a same serial number for two or more different frames. It is clear that this will cause a multitude of management problems, because an important means for identifying a vehicle would be lost. The traditional control method for not misnumbering a frame has been to depend on the press operator to visually check the number against the scheduled listing, for example, as each frame is stamped.
This method of control has the following disadvantages.
(1) The computer generated frame numbers are given out to the operator on the basis of a weekly production of an assembly line (hereinafter referred to as the line). This is because the production planning is usually based o monthly production requirements, and from this monthly data in the main computer is obtained a weekly figure for the line production which is given out to the operator. PA0 (2) The frame numbers generated in the main computer are forwarded to stamping machine(s), which stamps numbers automatically on the frames. If nothing disrupts the sequence of the stamping operation, then a proper frame number is stamped on a correct frame. However, when there is a change in the production schedule, so that a frame number is in abeyance, then there is a discrepancy between the frame on the line and the number in the stamping machine. Unless checked, a wrong frame number is stamped. Therefore, it becomes essential for the press operator to check his operation closely to avoid misstamping. The problem is that human errors are unavoidable. PA0 (3) In such a computer-managed production line, when some component is lacking, a certain batch of cars cannot be produced, and this lot must be set aside away from the line. When this happens, the entire production schedule must be reorganized, including the frame numbers which have been pre-assigned according to the original weekly schedule set by the main computer. It then necessitates regrouping of the frame numbers according to new input data from the individual production control centers. This re-scheduling data entry into the main computer is performed manually and presented an undesirably deficient situation. PA0 (4) The system described above is based on a centralized control concept, and it is difficult to provide redundancy for frame number management. If there is a problem in the main computer, there is a danger of disabling the entire production line. Therefore, from the viewpoint of the overall efficiency, this type of system lacked dependability. Furthermore, since the system is based on a top-down command structure from the upstream computer, if there is a change in the production scheduling, manual data entry is required, making the whole system vulnerable.
Under ordinary circumstances, the continuity of successive frame numbers can be assured. However, due to various human errors in computer operation, the continuity of the frame numbers can, sometimes, be interrupted. When this happens, the chances of doubling or missing frame numbers are increased. It is, therefore, crucial to check the continuity of the frame numbers, but the conventional human method of checking is quite inadequate. Additionally, the recent production trend of a mixed-mode production, i.e. a variety of different models handled within the same line, requires a greater necessity for the serial continuity of a given model. This checking requires a large degree of human effort, leading to high potential for causing misses.